LED light bulbs which use, as a light source, a light emitting diode (LED) corresponding to a semiconductor light emitting element have been used as lighting apparatuses that replace incandescent light bulbs. In LED light bulbs, a board on which an LED is mounted is attached to a metal base, a surface of the base on the light source side is covered with a translucent globe, and a surface of the base on the opposite side is provided with a housing which has a thermally radiative structure. A cap is provided at one end of the housing. In the cap, a power source circuit which supplies electric power to the LED is provided. In LED light bulbs having the above structure, heat is radiated mainly from the external surface of the housing. There are LED light bulbs in which a number of fins are provided on the external surface of the housing to improve thermally radiative performance.
However, it is difficult for thermal radiation from the external surface of the housing to suppress an increase in temperature of LEDs which radiate a greater amount of heat. When the housing is formed of a material which has high thermal conductivity to improve thermally radiative performance, the power source circuit is held in the housing, thus the temperature of the power source circuit increases, and there is a risk that the power source circuit may be destroyed by heat.
In addition, there are LED light bulbs which have fins which project radially from the external surface of the housing. The LED light bulbs have high thermally radiative performance, but instead are larger than regular incandescent light bulbs. Therefore, such LED light bulbs cannot be used instead of incandescent light bulbs, and have only limited uses. In addition, since the projecting fins block light from LEDs, and thus the luminous intensity distribution angle of the light bulbs are limited.